Thermoelectric device

ABSTRACT

A thermoelectric device ( 1 ) comprising a frame ( 2 ), a membrane ( 3 ) made of thermoelectric material, and an element ( 4 ) for absorbing or releasing energy. The element ( 4 ) is supported to the frame ( 2 ) solely by the membrane ( 3 ).

This application is the U.S. national phase of International ApplicationNo. PCT/FI2017/050142 filed 3 Mar. 2017, which designated the U.S. andclaims priority to FI Patent Application No. 20165190 filed 7 Mar. 2016,the entire contents of each of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to a thermoelectric device.

BACKGROUND OF THE INVENTION

Thermoelectric devices may be used as components of apparatuses whereina thermoelectric effect is utilized. The thermoelectric effect refers toa direct conversion of temperature differences to electric voltage orvice versa. In thermoelectric effect charge carriers operate as heatcarriers.

A prior art thermoelectric device comprises a membrane made ofthermoelectric material. The thermoelectric device creates voltage whenthere is a temperature difference on each side. Conversely, atemperature difference may be created in response to a voltage appliedto the thermoelectric device. The thermoelectric devices can thereby beused for example to generate electricity or to change temperature ofobjects.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a novel thermoelectricdevice.

The invention is characterized by the features of the independent claim.

A thermoelectric device comprises a frame, a membrane made ofthermoelectric material and an element for absorbing or releasingenergy, the element being supported to the frame solely by the membrane.

In the thermoelectric device disclosed the element is supported to theframe solely by the membrane which provides an active element ofthermoelectric device. So, there are no additional components ormaterials which are attached to the element so as to support the elementto the frame. This means that electro-thermal performance of thethermoelectric device may be optimized by characteristics of themembrane. Some embodiments of the invention are disclosed in dependentclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of preferred embodiments with reference to the accompanyingdrawings, in which

FIG. 1 shows schematically a thermoelectric device obliquely from above;

FIG. 2 shows schematically a cross-sectional side view of athermoelectric device according to FIG. 1;

FIG. 3 shows schematically a cross-sectional side view of a secondthermoelectric device;

FIG. 4 shows schematically a cross-sectional side view of a thirdthermoelectric device;

FIG. 5 shows schematically a fourth thermoelectric device from below;

FIG. 6 shows schematically a top view of a fifth thermoelectric devicefrom below;

FIG. 7 shows schematically a cross-sectional side view of thethermoelectric device of FIG. 6,

FIG. 8 shows schematically an example of a radiation meter;

FIG. 9 shows schematically an example of a thermoelectric coolingstructure; and

FIG. 10 shows schematically an example of an energy harvester.

For the sake of clarity, the figures show some embodiments of theinvention in a simplified manner. Like reference numerals identify likeelements in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically a thermoelectric device 1 obliquely fromabove. FIG. 2 shows schematically a cross-sectional side view of athermoelectric device 1 according to FIG. 1 along a line A-A shown inFIG. 1. Thermoelectric device 1 may be used as a component in anapparatus wherein a thermoelectric effect is utilized.

The thermoelectric device 1 comprises a frame 2 having a first side 2 a,a second side 2 b, a third side 2 c and a fourth side 2 d, the number ofthe sides of the frame 2 varying depending on the actual implementationof the frame 2. Further the thermoelectric device 1 comprises a membrane3 made of thermoelectric material and attached to the frame 2. Themembrane 3 may consist of different materials. Furthermore thethermoelectric device comprises an element 4 for absorbing or releasingenergy, i.e. an energy absorber 4 or emitter 4, or in other words, anelement 4 capable of absorbing or releasing energy. The element 4 issuspended to the membrane 3 and is supported to the frame 2 solely bythe membrane 3.

The membrane 3 of FIG. 1 is patterned to comprise two first beams 5 a, 5b and two second beams 6 a, 6 b and a contacting region 7 for contactingthe beams 5 a, 5 b, 6 a, 6 b to each other. First ends of the beams 5 a,5 b, 6 a, 6 b are attached to the frame 2 for supporting the membrane 3to the frame 2 and second ends of the beams 5 a, 5 b, 6 a, 6 b areattached to the contacting region 7. The beams 5 a, 5 b, 6 a, 6 b andthe contacting region 7 may be one uniform membrane structure made of asingle membrane billet or the beams 5 a, 5 b, 6 a, 6 b and thecontacting region 7 may be originally separate parts that are attachedto each other so as to form one uniform membrane structure. A number ofmembrane-free regions 8 remains between the frame 2 and the membrane 3.

According to an embodiment of the thermoelectric device 1 of FIG. 1, thefirst beams 5 a, 5 b each are configured to comprise at least one n-typeregion and the second beams 6 a, 6 b each are configured to comprise atleast one p-type region. The n-type region refers to a region wherein aconcentration of conducting electrons is very high or where the Seebeckcoefficient is different from that of the p-type region. The p-typeregion refers to a region wherein a concentration of holes is very highor where the Seebeck coefficient is different from that of the n-typeregion. Concentration of holes/electrons produced by doping is alsoreferred to with a term p-doped/n-doped. Highly doped n-type and p-typeregions may also be denoted with a marking n++ and p++, respectively.

The contacting region 7 is configured to connect the above mentionedregions to each other.

According to an embodiment of the thermoelectric device 1, thecontacting region 7 is configured to connect the first beams 5 a, 5 band the second beams 6 a, 6 b to each other pair by pair, but theconnection configuration is not limited to this. In this embodiment, forexample, the beam 5 a may be connected to the beam 6 a to contact the atleast one n-type region in the beam 5 a to the at least one p-typeregion in the beam 6 a, and the beam 5 b may be connected to the beam 6b to contact the at least one n-type region in the beam 5 b to the atleast one p-type region in the beam 6 b.

According to an embodiment of the thermoelectric device 1, both thefirst beams 5 a, 5 b each and the second beams 6 a, 6 b each areconfigured to comprise at least one n-type region, and the contactingregion 7 is configured to connect the at least one n-type regionremaining in some beam to the at least one n-type region remaining insome another beam.

According to an embodiment of the thermoelectric device 1, both thefirst beams 5 a, 5 b each and the second beams 6 a, 6 b each areconfigured to comprise at least one p-type region, and the contactingregion 7 is configured to connect the at least one p-type regionremaining in some beam to the p-type region remaining in some anotherbeam.

According to an embodiment of the thermoelectric device 1, both thefirst beams 5 a, 5 b each and the second beams 6 a, 6 b each areconfigured to comprise both at least one n-type region and at least onep-type region, and the contacting region 7 is configured to connect theat least one n-type region remaining in some beam to the at least onep-type region remaining either in the same beam or in some another beam.

According to an embodiment of the thermoelectric device 1, thethermoelectric device 1 comprises one first beam and one second beamwhich are connected to each other by the contacting region. The beamsmay be arranged to comprise the at least one n-type region and the atleast one p-type region in any manner as disclosed above or below.

As a summary of the embodiments mentioned above, it may be said that themembrane is patterned to comprise at least one first beam and at leastone second beam, the at least one first beam and the at least one secondbeam being arranged to support the element to the frame. The at leastone first beam is arranged to comprise at least one n-type region and/orat least one p-type region, i.e. at least one of at least one n-typeregion and at least one p-type region. Furthermore, the at least onesecond beam is arranged to comprise at least one n-type region and/or atleast one p-type region, i.e. at least one of at least one n-type regionand at least one p-type region.

In the embodiment of the thermoelectric device 1 disclosed in FIG. 1 themembrane 3 was patterned to comprise altogether four beams, but a numberof the beams may vary. In its minimum there may be only one beam whichmay be configured to comprise at least one n-type region, or at leastone p-type region, or both at least one n-type region and at least onep-type region and a possible contacting region 7 for connection then-type and/or the p-type regions to each other. In its minimum tworegions with different thermoelectric properties are needed in order tohave finite total voltage.

The at least one n-type region and/or the at least one p-type region maybe configured to provide a part or all of the cross-sectional area ofthe beam 5 a, 5 b, 6 a, 6 b, whereby in the latter case it may also besaid that the beam 5 a, 5 b, 6 a, 6 b is formed of the at least onen-type region and/or the at least one p-type region.

Furthermore, according to an embodiment of the thermoelectric device 1the membrane 3 does not comprise any beams but the membrane 3 isconfigured to extent uniformly over a whole free area being confined bysides of the frame, whereby the membrane 3 extends at all its sidesuniformly up to the frame 2 so that there are no intentionalmembrane-free areas 8 in the area confined by the frame. In that casethe membrane 3 may also be configured to comprise at least one n-typeregion, or at least one p-type region, or both at least one n-typeregion and at least one p-type region and a possible contacting region 7for connection the n-type and/or the p-type regions to each other.

The frame 2 may for example be a silicon frame. Portions of the membrane3, such as the beams 5 a, 5 b, 6 a, 6 b, comprising the at least onen-type region and/or the at least one p-type region may be formed of forexample amorphous, or single crystalline or polycrystalline silicon. Thefirst beams 5 a, 5 b and the second beams 6 a, 6 b can be of differentmaterials.

A portion of the membrane 3 comprising the contacting region 7 may beformed of for example metal or semiconductor material or a semimetal orsome combination thereof, such as aluminium Al, molybdenum Mo, titaniumwolfram TiW, titanium nitride TiN, silicon nitride SiN, dopedsemiconductor or Graphene. The contacting region may also containdielectric or nonconductive semiconductor parts, such as SiO2, SiN orweakly or un-doped semiconductors.

According to an embodiment the membrane 3 may be microfabricated fromthe frame 2.

The element 4 for absorbing or releasing energy may be a metal, or asemiconductor or a semimetal or a dielectric or some combinationthereof, such as aluminium Al, molybdenum Mo, titanium wolfram TiW,titanium nitride TiN, silicon nitride SiN, doped or undopedsemiconductor, Graphene or porous silicon. The contacting region 7 andthe element 4 may be made of same material and region 7 and element 4may contain holes. Some practical implementations of the element 4 aredisclosed later when some practical applications of the thermoelectricdevice 1 are disclosed.

In the thermoelectric device 1 temperature difference between thecentral part of the membrane 3 containing the element 4 and the frame 2creates the electrical signal. Typically the frame 2 is maintained atconstant temperature. The temperature difference causes charge carriersin the material to diffuse from a hot side to a cold side.

If the membrane 3 is configured to comprise only at least one n-typeregion or at least one p-type region, a voltage difference recognizableis yet achievable at least if membrane materials with differentthermoelectric properties are applied on the at least one n-type regionor the at least one p-type region.

Alternatively, when connecting a power supply to the thermoelectricdevice 1, temperature difference may be generated between the centralpart of the membrane 3 containing the element 4 and the frame 2, i.e.between the contacting region 7 and the frame 2. In that case thethermoelectric device 1 may be utilized for heating or cooling purposes,depending on the polarity of the connection between the power supply andthe thermoelectric device 1.

The general operating principle of the thermoelectric effect and thethermoelectric devices utilizing the thermoelectric effect is known assuch for a person skilled in the art and therefore it is not disclosedherein in more detail.

In the thermoelectric device 1 disclosed the element 4 is supported tothe frame 2 solely by the membrane 3, i.e. there are no additionalcomponents or materials which are attached to the element 4 so as tosupport the element 4 to the frame 2. This means that the element 4 issupported to the frame 2 only by the active element, i.e. the membrane3, of the thermoelectric device 1 so that it is solely the membrane 3that is attached to the element 4, or in other words, the element 4 isattached solely to the membrane 3 for supporting the element 4 to theframe 2. This means that the electro-thermal performance of thethermoelectric device 1 may be optimized by characteristics of themembrane 3. The patterning of the membrane 3 to comprise beams 5 a, 5 b,6 a, 6 b is one option to effect on the operation characteristics, suchas a sensitivity, of the thermoelectric device 1. The number of thebeams 5 a, 5 b, 6 a, 6 b in the membrane 3 is one feature which effectson a stability of the element 4 in the thermoelectric device 1.

A sensitivity of the thermoelectric device 1, i.e. an ability of thethermoelectric device 1 to convert a temperature difference appearing inthe membrane 3 to electric voltage, or to utilize electric voltageapplied to the thermoelectric device 1 for heating or cooling purposes,is expressed by thermoelectrical figure-of-merit ZT:ZT=(S ²σ/κ)T,  (1)wherein S is a Seebeck coefficient [V/K] describing a thermoelectricsensitivity of material, σ is electrical conductivity [S] describingmaterial's ability to conduct an electric current, κ is thermalconductivity [W/mK] describing a property of the material to conductheat and T is the average temperature [K]. For increasing thefigure-of-merit ZT of the thermoelectric unit 1 the electricalconductivity σ of the at least one the n-type region and/or the at leastone p-type region 6 should be increased and/or the thermal conductivityκ of the at least one the n-type region and/or the at least one p-typeregion should be decreased. Also the Seebeck coefficient S should bemaximized, for example by a proper material selection.

According to an embodiment of the thermoelectric unit 1, theconcentration of the electrons, i.e. n++-concentration, in the at leastone n-type region, and/or the concentration of the holes, i.e.p++-concentration, in the at least one p-type region, is at least1E18/cm³, such as 1E18/cm³-5E18/cm³. Preferably the n++-concentrationand/or the p++-concentration is at least 1E19/cm³. More preferably then++-concentration and/or the p++-concentration is at least 1E20/cm³, forexample between 1E20/cm³-1E21/cm³.

According to an embodiment of the thermoelectric unit 1, a thickness ofthe at least one n-type region and/or the at least one p-type region isless than 50 nm. Preferably the thickness of the at least one n-typeregion and/or the at least one p-type region is less than 40 nm, andmore preferably less than 20 nm. When the thickness of the at least onen-type region and/or the at least one p-type region is very small, i.e.few tens of nanometres, the thermal conductivity of the at least onen-type region and/or the at least one p-type region is low due toreduced phonon heat conduction of the membrane 3 at the n-type regionand/or the p-type region.

FIG. 3 shows schematically a cross-sectional side view of a secondthermoelectric device 1. The thermoelectric device 1 of FIG. 3 issubstantially the same as the thermoelectric device 1 of FIG. 2, but inthe embodiment of FIG. 3 the membrane 3 is covered by a passivationlayer 9. The thickness of the passivation layer is considerably smallerthan the thickness of the membrane 3, the only purpose of thepassivation layer 9 being to passivate the surface to prevent aging ofthe thermoelectric material and protect it. The passivation layer 9 maybe made of for example silicon dioxide, silicon nitride, aluminium oxideor polymer and it may consist of two or more sublayers laid one on theother so that the sublayers together form the passivation layer 9. Ifthe passivation layer 9 comprise sublayers, some of the sublayers may beof the same material. Passivation layer can be different for differentparts of the membrane 3. Native oxides of the membrane 3 materials mayprovide a sufficient passivation.

FIG. 4 shows schematically a cross-sectional side view of a thirdthermoelectric device 1. The thermoelectric device 1 of FIG. 4 isotherwise similar to that of FIG. 2 but the thermoelectric device 1 ofFIG. 4 further comprises a full back reflector 10 below the element 4.

The full back reflector 10 is arranged to extend up to all sides 2 a, 2b, 2 c, 2 d of the frame 2 so that there are no intentional open areasbetween the full back reflector 10 and the sides 2 a, 2 b, 2 c, 2 d ofthe frame 2. The full back reflector 10 may be replaced with a partialback reflector, whereby there may be some open areas between the fullback reflector 10 and the sides 2 a, 2 b, 2 c, 2 d of the frame 2. Thepurpose of the full back reflector 10 and the partial back reflectorarranged below the element 4 is to reflect radiation passed through themembrane 3 back towards the element 4.

Alternatively to the full or partial back reflector or in addition tothem the thermoelectric device 1 may also comprise a partial frontreflector 11 above the element 4 as also shown in FIG. 4, the partialfront reflector 11 leaving open areas between the reflector 11 and theframe 2. The purpose of the front reflector 11 is to reflect radiationtowards the membrane 3 and the element 4 suspended to the membrane 3.

The distance of the back reflector 10 and/or the front reflector 11 isoptimized at a preferred distance from the element 4. Typically thedistance of the back and/or front reflector from the element is set tobe about a quarter of a wavelength of the radiation intended to beabsorbed by the thermoelectric device 1, or a multiple of the quarter ofthe wavelength of the radiation.

FIG. 5 shows schematically a fourth thermoelectric device 1 from below.The thermoelectric device 1 of FIG. 5 comprises a frame 2 and a membrane3 made of thermoelectric material. The membrane 3 comprises beams 5 a, 5b, 6 a, 6 b and a connecting region 7 as well as an element 4 suspendedto the membrane 3. The membrane-free areas are again denoted with thereference number 8. In the thermoelectric device 1 of FIG. 5 the portion12 of the membrane 3 denotes an unpatterned part of the membrane 3 thatextends from the beams 5 a, 5 b, 6 a, 6 b up to the sides 2 a, 2 b, 2 c,2 d of the frame 2. The membrane 3, the element 4 and the contactingregion 7 may be made of material that has mechanical properties whichcause the material to contract or to strain for keeping the membrane 3,the element 4 and the contacting region 7 straight.

FIG. 6 shows schematically a top view of a fifth thermoelectric device 1from below. FIG. 7 shows schematically a cross-sectional side view ofthe thermoelectric device of FIG. 6 along a line B-B shown in FIG. 6.

The thermoelectric device 1 of FIGS. 6 and 7 comprises a frame 2 and amembrane 3 made of thermoelectric material. The membrane 3 comprisesbeams 5 a, 5 b, 5 c, 5 d 6 a, 6 b, 6 c, 6 d and a connecting region 7 aswell as an element 4 suspended to the membrane 3. The membrane 3 furthercomprises the unpatterned part 12 of the membrane 3 to which first endsof the beams 5 a, 5 b, 5 c, 5 d 6 a, 6 b, 6 c, 6 d of the membrane 3 areattached to, the first ends of the beams 5 a, 5 b, 5 c, 5 d, 6 a, 6 b, 6c, 6 d being the ends of the beams pointing towards the sides 2 a, 2 b,2 c, 2 d of the frame 2. The membrane-free areas are again denoted withthe reference number 8.

The thermoelectric device 1 of FIGS. 6 and 7 also comprises a straintuning layer 13 that has the circumferential shape and remains betweenthe membrane 3 and the frame 2 surrounding the membrane 3. The straintuning layer 13 provides an element which suspends the membrane 3 to theframe 2 so that the membrane and/or beams are retained straight or flatby pulling the membrane and/or the beams. The strain tuning layer 13 maybe made of silicon nitride, for example, whereby the strain tuning layer13 is thermodynamically stable and able to retain the membrane/beamsstraight in varying temperatures. An outer circumference of theunpatterned portion 12 of the membrane 3 is attached to the frame 2 andto the strain tuning layer 13. An outer circumference of the straintuning layer 13 is attached to the sides 2 a, 2 b, 2 c, 2 d of the frame2. The strain tuning layer 13 may also extend partially on top of thebeams, but still not reaching up to the element 4, as schematicallyshown in FIGS. 6 and 7.

In the embodiment of FIG. 6 the strain tuning layer 13 provides a straincontrol element which suspends the membrane 3 to the frame 2 so that themembrane and/or beams are retained straight. In spite of the usage ofthe strain tuning layer 13, the element 4 is supported to the frame 2solely by the membrane 3, i.e. only the membrane 3 and not anyadditional component or material is attached to the element 4 forsupporting the element 4 to the frame 2.

FIGS. 8, 9 and 10 disclose schematically some examples of apparatuseswherein the thermoelectric devices 1 as disclosed may be used. This kindof apparatuses may comprise one or more thermoelectric devices, thefollowing example apparatuses showing, for a sake of clarity, only onethermoelectric device 1. In the apparatuses the n-type regions and thep-type regions are connected through at least one electric circuit 14that is external to the thermoelectric device 1. Typically thethermoelectric device 1 comprises a number of poles to which the ends ofthe electric circuit 14 are connected to, but in the schematic Figuresthe ends of the electric circuit 14 are connected to the n-type andp-type regions.

FIG. 8 shows schematically an example of a radiation meter 15. In theradiation meter 15 the element 4 is an absorber for absorbing radiation.The absorber may be made of for example black silicon or black metal,such as black oxide coated metal, or a thin metallic multilayer grid, ora combination thereof or an optically matched multilayer or any othersurface structure that enhances the absorption of the desired wavelengthor range of wavelengths.

The radiation meter is configured to measure energy and/or power ofradiation received by the absorber on the basis of change in electriccurrent in the electric circuit 14 or a voltage difference formedbetween the central part of the membrane and the frame. The radiationmeter 15 may comprise a meter 16 for measuring either electric currentin the electric circuit 14 or the voltage difference between the centralpart of the membrane and the frame.

The radiation meter may be a bolometer, a calorimeter or the like forexample. The frequency range of the electromagnetic radiation may rangefrom gigaherzes to hundreds of teraherzes without restricting to thisrange. Applications may be found in the fields of detection of infrared,X-ray, visible light, THz-range or the like radiation.

A sensitivity of the radiation meter is described by noise equivalentpower NEP. For a thermoelectric device below the thermal cut-offNEP=NEPG (1+1/ZT)^(1/2),  (2)whereinNEPG=(4k_(B)GT²)^(1/2),  (3)

wherein k_(B) is Bolzmann constant [J/K] and G is a thermal conductance[W/mK] of the n-type and/or p-type regions. The thermal conductance Gfor the n-type and/or p-type regions is dependent on the cross-sectionalarea of the n-type and/or p-type regions as well as length thereof. Inorder to maximize the sensitivity of the radiation meter the noiseequivalent power NEP should be minimized.

In order to minimize the noise equivalent power NEP of the radiationmeter the value of ZT should be maximized. Therefore the electricalconductivity σ of the n-type and/or p-type regions should be maximized.This may be implemented by providing a concentration of electrons and/orholes as disclosed above. Also the Seebeck coefficient S should bemaximized, as disclosed above in connection with formula (1).

Furthermore, in order to minimize the noise equivalent power NEP of theradiation meter NEPG should be minimized by minimizing G. The smaller isthe value of G, the smaller is the thermal cut-off, and, therefore, thevalue of G typically must be optimized for each application case. ZT ismaximized and G is minimized by minimizing the thermal conductivity κ ofthe n-type and/or p-type regions. In order to minimize the thermalconductivity of the n-type and/or p-type regions, that may beimplemented by minimizing the phonon thermal conductivity of the n-typeand/or p-type regions by minimizing a thickness of the n-type and/orp-type regions as disclosed above.

FIG. 9 shows schematically an example of a thermoelectric coolingstructure 17 comprising at least one thermoelectric device 1. In thethermoelectric cooling structure 17 the element 4 is at least part of adevice to be cooled or a part connected to a device to be cooled. Cooleddevice may have electrical and/or optical connections to the frame or toother thermal path.

In the thermoelectric cooling structure 17 a voltage source 18 isconnected through the electric circuit 14 to the at least onethermoelectric device 1 so as to provide Peltier effect to take place.In a junction between the membrane 3 and the element 4 heat istransferred away from the element 4, which is intended to become hot dueto heat received from the device to be cooled and/or from thesurroundings and the ambient. The heat received to the membrane 3 fromthe element 4 may be transferred out of the thermoelectric device 1 witha heat sink, for example.

FIG. 10 shows schematically an example of an energy harvester 19. In theenergy harvester 19 the element 4 is a hot or cold element configured toabsorb or release thermal energy. According to an embodiment the atleast one thermoelectric unit 1 is connected through the electriccircuit 14 to an electric energy storage component 20 intended toprovide at least a short-term storage for electric energy. Some possiblepractical embodiments of the electric energy storage components 20 arefor example a supercapacitor or a rechargeable battery.

It will be obvious to a person skilled in the art that, as thetechnology advances, the inventive concept can be implemented in variousways. The invention and its embodiments are not limited to the examplesdescribed above but may vary within the scope of the claims.

The invention claimed is:
 1. A thermoelectric device comprising a frame,a membrane made of thermoelectric material and providing an activeelement of the thermoelectric device, and an absorbing element forabsorbing or releasing energy, the absorbing element being supported tothe frame solely by the membrane.
 2. A thermoelectric device as claimedin claim 1, wherein the membrane comprises at least one n-type regionand/or at least one p-type region.
 3. A thermoelectric device as claimedin claim 2, wherein the at least one n-type region and/or the at leastone p-type region are formed of amorphous, single crystalline orpolycrystalline silicon.
 4. A thermoelectric device as claimed in claim3, wherein a concentration of electrons or holes is at least 1E18/cm³.5. A thermoelectric device as claimed in claim 2, wherein thickness ofthe n-type region and/or the p-type region is less than 50 nm,preferably less than 40 nm, more preferably less than 20 nm.
 6. Athermoelectric device as claimed in claim 1, wherein the membranecomprises at least one n-type region, at least one p-type region and atleast one contacting region for contacting at least one region with atleast one another region.
 7. A thermoelectric device as claimed in claim1, wherein the membrane is patterned to comprise at least one first beamand at least one second beam, the at least one first beam comprising atleast one n-type region and/or at least one p-type region, and the atleast one second beam comprising at least one n-type region and/or atleast one p-type region, the at least one first beam and the at leastone second beam arranged to support the absorbing element to the frame.8. A thermoelectric device as claimed in claim 1, wherein thethermoelectric device comprises at least one strain tuning layer forretaining the membrane and/or beams straight or flat.
 9. Athermoelectric device as claimed in claim 1, wherein the absorbingelement for absorbing or releasing energy is a metal, a semiconductor ora dielectric, or a combination of those.
 10. A thermoelectric device asclaimed in claim 1, wherein the membrane is covered by a passivationlayer.
 11. A thermoelectric device as claimed in claim 1, wherein thethermoelectric device comprises a full or partial back reflectorarranged below the absorbing element to reflect radiation passed throughthe membrane back towards the element.
 12. A thermoelectric device asclaimed in claim 11, wherein the thermoelectric device comprises apartial front reflector.
 13. A radiation meter, wherein the radiationmeter comprises at least one thermoelectric device as claimed in claim1, wherein the absorbing element is an absorber for absorbing radiation,the radiation meter being configured to measure energy and/or power ofradiation received by the absorber.
 14. A thermoelectric coolingstructure, wherein the thermoelectric cooling structure comprises atleast one thermoelectric device as claimed in claim 1, wherein theabsorbing element is at least part of a device to be cooled or a partconnected to a device to be cooled.
 15. An energy harvester, wherein theenergy harvester comprises at least one thermoelectric device as claimedin claim 1, wherein the absorbing element is a hot or cold elementconfigured to absorb or release thermal energy.